Age hardening type bainitic microalloyed steels are a kind of steel configured so that the steel is soft when worked but increases in strength when heated, after the working, to a temperature not higher than a transformation temperature (age hardening treatment), without undergoing a heat-treatment strain. Consequently, such steels are being developed as microalloyed steels which combine strength and machinability. For example, the following Patent Documents 1 and 2 disclose such age hardening type bainitic microalloyed steels combining strength and machinability.
Patent Document 1: JP-A-2011-236452
Patent Document 2: JP-A-2015-180773